Cystatin C and blood pressure: results of 24 h ambulatory blood pressure monitoring

Background: The relationship between kidney function and blood pressure (BP) components has been studied in chronic kidney disease patients. Whether cystatin C, a marker of kidney function, is associated in the normal range with systolic BP (SBP), diastolic BP (DBP), and pulse pressure (PP) obtained using ambulatory blood pressure monitoring has not been previously studied.

Methods: The sample subjects were 53 males and 34 females, mean age was 59.3+/-13.5 years. 76% were receiving antihypertensive drug treatment. Kidney function was evaluated by measuring serum cystatin C. Microalbuminuria was measured in a 24h urine collection. Glomerular filtration rate (GFR) was estimated using the abbreviated Modification of Diet in Renal Disease equations. The ambulatory BP was measured non-invasively for 24h by the Spacelab devices programmed to measure BP every 15 min during daytime and every 20 min during nighttime.

Results: The highest quartile of cystatin C distribution showed an older age and worsel parameters of renal function (cystatin C, serum creatinine and GFR) than the other groups. No differences for gender or diabetes were found. 24h SBP and PP were higher in the fourth quartile compared to the fist one (p<0.01). 24h DBP was lower for the patients in the fourth quartile of cystatin C compared which any one of the other groups (p<0.001). The relationship between cystatin C, as well as GFR, with SBP and PP was statistically significant as renal function comes down. Contrariwise, as cystatin C increases DBP declines; but the correlation with GFR measured through MDRD 4 is not significant. In the same way, no correlation was found for GFR and microalbuminuria, but there was a statistically significant positive relationship between cystatin C and microalbuminuria severity (p<0.01). Multivariate regression analysis confirms these findings.

Conclusions: Both SBP and pulse pressure were significantly associated with kidney function. DBP was negatively correlated with cystatin C concentrations but not with GFR. Cystatin C shows a positive relationship with microalbuminura severity. Cystatin C might have cardiovascular effects beyond its use as a marker of the renal function.